First-principles investigation of W[sbnd]V and W[sbnd]Mo alloys as potential plasma facing materials (PFMs) for nuclear application

Density-functional theory (DFT) based first-principles calculations were used to investigate the crystal structure, binding energy, phase stability and elastic properties of body-centered cubic (BCC) W-based binary solid solutions. The effect of alloying up to 50 atomic percent (at.%) concentration range is determined from the virtual-crystal approximation (VCA) approach. Resulting BCC solid solutions are assessed in comparison to the ideal Vegard's law. Solubility of the alloying elements is characterized by the negative enthalpy of mixing. The values of elastic constants computed for the ground state structures are used to assess the effect of alloying on the ductility and hardness. Based on current results, it seems key to strike a tricky balance between moderate Pugh's modulus ratio (B/G) between bulk and shear moduli (B,G) and elastic anisotropy (A) such that high hardness is not completely compromised at the expense of ductility

Structural characterization of mechanically milled and annealed tungsten powder

Abstract Nanocrystalline W powders with an average crystallite size of about 50 nm were produced by mechanical milling. BCT phase was mechanically induced as a result of BCC lattice deformation (compression) along [110], upon 10 h, 20 h and 30 h milling corresponding to a magnetic saturation of 1.3, 6.9, and 9.8 μTm3/kg. This BCT phase suggests the tetragonal deformation path to be responsible for the observed anomalous magnetism in W. Following DSC–TG thermal analysis, a magnetic saturation of 68 μTm3/kg was obtained upon annealing the 30 h milled W powder at 1200 °C. In addition, two BCT phases with c/a=1.313 (a=0.29066, c=0.38170 nm) and 0.907 (a=0.32602, c=0.29575 nm) were detected

Influence of Extrusion on the Microstructure and Mechanical Behavior of Mg-9Li-3Al-xSr Alloys

Mg-9Li-3Al-xSr (LA93-xSr, x = 0, 1.5, 2.5, and 3.5 wt pct) alloys were cast and extruded at 533 K (260° C) with an extrusion ratio of 28. The microstructure and mechanical response are reported and discussed paying particular attention to the influence of extrusion and Sr content on phase composition, strength, and ductility. The results of the current study show that LA93-xSr alloys contain both α-Mg (hcp) and β-Li (bcc) matrix phases. Moreover, the addition of Sr refines the grain size in the as-cast alloys and leads to the formation of the intermetallic compound (Al4Sr). Our results show significant grain refinement during extrusion and almost no influence of Sr content on the grain size of the extruded alloys. The microstructure evolution during extrusion is governed by continuous dynamic recrystallization (CDRX) in the α-Mg phase, whereas discontinuous dynamic recrystallization (DDRX) occurs in the β-Li phase. The mechanical behavior of the extruded LA93-xSr alloy is discussed in terms of grain refinement and dislocation strengthening. The tensile strength of the extruded alloys first increases and then decreases, whereas the elongation decreases monotonically with increasing Sr; in contrast, hardness increases for all Sr compositions studied herein. Specifically, when Sr content is 2.5 wt pct, the extruded Mg-9Li-3Al-2.5Sr (LAJ932) alloy exhibits a favorable combination of strength and ductility with an ultimate tensile strength of 235 MPa, yield strength of 221 MPa, and an elongation of 19.4 pct